What is T4 (Thyroxine)?


What is T4 (Thyroxine)?

The thyroid hormone is important for the growth, development, and regulation of different metabolic processes in the body. In this article, you will learn what levothyroxine is, its mechanism of action, benefits, and side effects.


Levothyroxine (T4) is a synthetic version of thyroxine (T4), one of the natural thyroid hormones. It is administered when the a subject is deficient in thyroxine.

In animal test studies, it demonstrated its usefulness in treating severe hypothyroidism or myxedema coma, which originated in the thyroid, pituitary, or hypothalamus. It is also used to treat euthyroid goiters and thyroid cancer in animals that have undergone thyroidectomy and as an adjunct to surgery and radioiodine therapy.


IUPAC Name: (2S)-2-amino-3-[4-(4-hydroxy-3,5-diiodophenoxy)-3,5-diiodophenyl]propanoic acid

Molecular Formula: C15H11I4NO4

Molecular weight: 776.87 g/mol

CAS number: 51-48-9


Normally in animal test subjects, the hypothalamus secretes thyrotropin-releasing hormone (TRH), which stimulates the anterior pituitary to secrete thyroid-stimulating hormone (TSH). The TSH subsequently stimulates the thyroid to secrete 80% thyroxine (T4) and 20% L-triiodothyronine (T3). 50% of thyroxine (T4) then gets converted to its active metabolite L-triiodothyronine (T3). The thyroid hormones bind to thyroid receptor proteins contained within the cell nucleus.

Once inside the nucleus, thyroid hormones directly influence DNA transcription to increase metabolism by increasing gluconeogenesis, protein synthesis, etc. In situations like primary, secondary, or tertiary hypothyroidism, where this process is interrupted, levothyroxine may mimic endogenous T4 production by the thyroid.

T4 is absorbed from the gastrointestinal tract. Its absorption is increased by fasting and decreased in certain malabsorption syndromes, by certain foods, and with age.


Studies showed that animal models which were treated with levothyroxine were less likely to develop diseases like Addison’s disease, bipolar disorder, chronic kidney disease, depression, migraine, obesity, type 1 diabetes or type 2 diabetes.

A recent study on rats with Alzheimer’s Disease showed that injections of levothyroxine alleviated memory deficits and improved levels of Brain-Derived Neurotrophic Factor (BDNF). These results demonstrated that low-dose levothyroxine improved deficits in learning and memory in those rats.


You can purchase levothyroxine from Loti Labs. It is important to buy research liquids which are USA-made, to ensure the integrity of your research. Levothyroxine is tested to ensure quality. It is available in liquid form and is commonly sold in 100mcg per ml vials.


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